Think of it like a family.
Say you have yourself (first name, last name, address, etc.), and you want to find all of your relatives with the same last name, so to do that you compare your last name to all of their last names. This will give you a list of all of your family members with the same last name. That relation contains all of details (rows) of each person (row) you are related to. What that means is that the contents of a relation are not just one piece of information (column), it’s the entire row.
What I’m getting at, is that the quickest way to know that you are related to someone is by having the same last name. That’s your relation. Once you have your relation, then you can determine their first name or their address by using a Lookup to find a specific column. Or you can just use an inline list to display any pieces of information from that relation.
Like @shchc mentioned, what shows in a relation column is mostly irrelevant. It just shows you that a match was found based on the columns you chose to match up. There is no way for a relation to predict what you want to see or what you want to use it for, so it just picks a column value to show you. Also, it would be overwhelming if a relation column showed the entire contents of a row, especially if you have 10’s or 100’s of columns in each row.